Wireless communication control channel apparatus and method

ABSTRACT

An apparatus and method for control channel transmission in a wireless network are disclosed. A disclosure is provided with at least one resource block (RB) including a first control channel element associated with a first antenna port (AP) and a second control channel element associated with a second AP. The first and second control channel elements might be used for transmission of a single control channel, and a first reference signal sequence associated with one of the first AP and the second AP is selected for transmission of the single control channel based on a control channel element index value, such that a resource element of the at least one RB can be detected to decode the first control channel element and the second control channel element.

This application is a continuation application of U.S. Non-Provisionalapplication Ser. No. 13/628,648 filed on Sep. 27, 2012, entitled“Wireless Communication Control Channel Systems and Methods,” whichclaims benefit of U.S. Provisional Application No. 61/540,678 filed onSep. 29, 2011, entitled “Wireless Communication Control Channel Systemsand Methods,” U.S. Provisional Application No. 61/555,994 filed on Nov.4, 2011, entitled “Wireless Communication Control Channel Systems andMethods,” U.S. Non-Provisional application Ser. No. 14/642,281 filed onMar. 9, 2015, entitled “Wireless Communication Control Channel Apparatusand Method,” and U.S. Non-Provisional application Ser. No. 14/986,480filed on Dec. 31, 2015, entitled “Wireless Communication Control ChannelApparatus and Method,” all of which are hereby incorporated herein byreference as if reproduced in their entireties.

TECHNICAL FIELD

The present invention relates to wireless communication apparatus andmethod, and, in particular embodiments, to wireless communicationcontrol channel apparatus and method.

BACKGROUND

Wireless communications networks often use a control channel tocommunicate control information (e.g., resource allocation, modulation,and coding information, etc.) pertaining to a data channel. Forinstance, third generation partnership project (3GPP) Long TermEvolution (LTE) release 10 (rel-10) specifies communicating controlinformation of a Physical Downlink Shared Channel (PDSCH) using aPhysical Downlink Control Channel (PDCCH). The PDCCH is located in thecontrol region of the sub-frame (which spans the first few leadingsymbols of the subframe), while the PDSCH is located in the data regionof the subframe (which spans the remaining/trailing symbols of thesubframe). Other control channels may also occupy the control region ofthe subframe. For instance, the control channel may include a PhysicalHybrid Indicator Channel (PHICH) for carrying acknowledgment (ACK) andnegative-acknowledgment (NACK) messages in response to uplink datatransmissions and a Physical Control Format Indicator Channel (PCFICH)for indicating the number of symbols of control region in a subframe.

One proposed modification for future releases of LTE (e.g., 3GPP LTE-Arelease 11 (rel-11), etc.) is the introduction of an enhanced PDCCH(E-PDCCH) in the downlink subframe. The E-PDCCH may be used to carryuplink (UL) and/or downlink (DL) control signaling regarding the PDSCHand/or the physical uplink shared channel (PUSCH) to user equipments(UEs). Unlike previous control channels, the E-PDCCH will be located (atleast partially) in the data region of the subframe, and may befrequency division multiplexed (FDM) with the PDSCH.

There may be multiple E-PDCCHs to communicate multiple control messagesin a single PRB pair using time-division-multiplexing (TDM) techniques,frequency division multiplexing (FDM) techniques, spatial divisionmultiplexing (SDM) techniques, or combinations thereof. This ability tocommunicate multiple resource allocations in a single RB is particularlybeneficial when high order modulation techniques are used, e.g., 16quadrature amplitude modulation (QAM), etc. When an RB (or RB-pair)carries multiple control messages using TDM or FDM techniques, it isnecessary to partition the RB (or RB-pair) by mapping available REs tomultiple control channel elements (CCE). In this disclosure, CCEs of theE-PDDCH may be referred to as enhanced CCEs (eCCEs). For instance, an RBor RB-pair may be partitioned between a first eCCE (eCCE0) and a secondeCCE (eCCE1).

It is desirable to evenly partition an RB (or RB pair) amongst themultiple eCCEs such that each eCCE is assigned/allocated the same numberof REs. However, evenly partitioning an RB amongst multiple eCCEs iscomplicated by the existence of overhead information (e.g., referencesignals, etc.) within the RB or RB pair carrying the E-PDCCH, which maybe used for, inter alia, channel estimation (e.g., fading, etc.).Notably, the number and position of the overhead REs in the RB or RBpair varies depending on the configuration of the downlink channel,which means that an even partitioning of the RB or RB-pair cannotgenerally be achieved through a simple bifurcation of the RB or RB pair(e.g., splitting the RB in half along the time domain or frequencydomain). That is to say, the sporadic and uneven interspersion ofoverhead REs within the RB or RB pair carrying the E-PDCCH would, moreoften than not, cause one of the halves to carry more overhead (andtherefore fewer available REs) than the other. As such, a mechanism ortechnique for evenly partitioning the E-PDCCH between two or moreresource allocations is desired.

SUMMARY

Technical advantages are generally achieved, by embodiments of thepresent invention which describe wireless communication control channelsystems and methods.

In one embodiment, a method for allocating resources in a wirelessnetwork is provided. In this example, the method includes transmitting acontrol channel in a resource block (RB) or RB-pair. The control channelcomprises a first control channel element that is associated with afirst antenna port and a second control channel element that isassociated with a second antenna port. The first antenna port ispre-assigned a first reference signal and the second antenna port ispre-assigned a second reference signal. The method further includesselecting one of the first reference signal and the second referencesignal, and transmitting the selected reference signal in the RB orRB-pair. The selected reference signal is transmitted to enable channelestimation for both the first control channel element and the secondcontrol channel element at a receiver side. An apparatus for performingthis method is also provided.

In another embodiment, a user equipment (UE) is in a wireless network isprovided. In this example, the UE is configured to receive a RB orRB-pair carrying a control channel that comprises a first controlchannel element associated with a first antenna port and a secondcontrol channel element associated with a second antenna port. The firstantenna port is pre-assigned a first reference signal and the secondantenna port is pre-assigned a second reference signal. The UE isfurther configured to identify either the first reference signal or thesecond reference signal as being selected for channel estimation, and toperform channel estimation using the selected reference signal to decodethe first control channel element and the second control channelelement.

In yet another embodiment, a method for communicating an enhancedPhysical Downlink Control Channel (E-PDCCH) is provided. In thisexample, the method includes communicating the E-PDCCH over a firstenhanced control channel element (eCCE) and a second eCCE of a resourceblock (RB) or RB-pair of a long term evolution (LTE) sub-frame. Thefirst eCCE corresponds to a first antenna port and the second eCCEcorresponds to a second antenna port. The first antenna port isassociated with a first demodulation reference signal (DMRS) and thesecond antenna port is associated with a second DMRS. The method furtherincludes determining that the first antenna port is selected for E-PDCCHdemodulation, and transmitting the first DMRS in the RB or RB-Pairwithout transmitting the second DMRS in the RB or RB-Pair, wherein thefirst DMRS is transmitted to enable channel estimation for both thefirst eCCE and the second eCCE.

In yet another embodiment, another method for allocating resources in awireless network is provided. In this example, the method includestransmitting a control channel in an RB or RB-pair. The control channelcomprises a first control channel element that is associated with afirst antenna port and a second control channel element that isassociated with a second antenna port. The first antenna port ispre-assigned a first reference signal and the second antenna port ispre-assigned a second reference signal. The method further includesassigning a first modified Walsh code to the first reference signal andassigning a second modified Walsh code to the second reference signal.The first modified Walsh code comprises a first complex constant thesecond modified Walsh code comprising a second complex constant. Thesecond complex constant and the first complex constant have a non-zerophase difference. The method further includes transmitting, in the RB orRB-pair, both the first reference signal in accordance with the firstmodified WALSH code and the second reference signal in accordance withthe second modified Walsh code. The first reference signal istransmitted to enable channel estimation for the first control channelelement and the second reference signal is transmitted to enable channelestimation for the second control channel element. An apparatus forperforming this method is also provided.

In yet another embodiment, another method for allocating resources in awireless network is provided. In this example, the method includestransmitting a control channel in a resource block (RB) or RB-pair. Thecontrol channel comprises a first control channel element and a secondcontrol channel element. The method further comprises associating thefirst control channel element with a first one of a plurality of antennaports having a first pre-assigned reference signal, identifying a secondone of the plurality of antenna ports having a second pre-assignedreference signal that does not overlap with the first pre-assignedreference signal in time-frequency domain, associating the secondcontrol channel element with the second antenna port, and transmittingthe first pre-assigned reference signal and the second pre-assignedreference signal in an overhead portion of the RB or RB-pair.

In yet another embodiment, a method for evenly partitioning a controlchannel between a first control channel element and a second controlchannel element is provided. In this example, the method includesidentifying available ones of a plurality of resource elements (REs) ofa resource block (RB) pair. The plurality of REs occupy a plurality oftime-slots spanning a plurality of sub-carrier frequencies. The methodfurther comprises allocating a first set of the available REs to thefirst control channel element. The first set of the available REsinclude all available REs that occupy: odd ones of the plurality oftimeslots spanning odd ones of the plurality of sub-carrier frequencies;and even ones of the plurality of timeslots spanning even ones of theplurality of sub-carrier frequencies. The method further includesallocating a second set of the available REs to the second controlchannel element. The second set of the available REs include allavailable REs that occupy: even ones of the plurality of timeslotsspanning odd ones of the plurality of sub-carrier frequencies; and oddones of the plurality of timeslots spanning even ones of the pluralityof sub-carrier frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a diagram of an embodiment of a wirelesscommunications network;

FIG. 2 illustrates a diagram of a block of time-frequency resources forcarrying wireless transmissions;

FIG. 3 illustrates a diagram of an embodiment of a RB that has beenpartitioned using a checkerboard partitioning technique;

FIG. 4 illustrates a diagram of another embodiment of a RB that has beenpartitioned using a derivative of the checkerboard partitioningtechnique;

FIG. 5 illustrates a diagram of an embodiment of a RB that has beenpartitioned using a derivative of the checkerboard partitioningtechnique;

FIG. 6 illustrates a diagram of the REs reserved for carrying DMRSsymbols corresponding to antenna ports 7, 8, 9, and 10 for a normalCyclic Prefix (CP) length;

FIG. 7 illustrates a diagram of a zero power problem that occurs in whenan RB (or RB-pair) carries two DMRSs corresponding to antenna ports 7and 8;

FIG. 8 illustrates a diagram of a zero power problem that occurs in anRB (or RB pair) carries two DMRSs corresponding to antenna ports 9 and10;

FIG. 9 illustrates a flowchart of an embodiment of a method for avoidingthe zero power problem when transmitting an RB or RB pair carrying anE-PDCCH that is associated with two antenna ports having overlappingreference signals;

FIG. 10 illustrates a flowchart of a method for receiving the RB or RBpair communicated by the method depicted in FIG. 9;

FIG. 11(a) illustrates a diagram of an embodiment of an RB or RB pairthat is communicated according to the method depicted in FIG. 9;

FIG. 11(b) illustrates a diagram of another embodiment of an RB or RBpair that is communicated according to the method depicted in FIG. 9;

FIG. 12(a) illustrates a diagram of yet another embodiment of an RB orRB pair that is communicated according to the method depicted in FIG. 9;

FIG. 12(b) illustrates a diagram of yet another embodiment of an RB orRB pair that is communicated according to the method depicted in FIG. 9;

FIG. 13 illustrates a flowchart of another embodiment of a method foravoiding the zero power problem when transmitting an RB or RB paircarrying an E-PDCCH that is associated with two antenna ports havingoverlapping reference signals;

FIG. 14(a) illustrates a diagram of an embodiment of an RB or RB pairthat is communicated according to the method depicted in FIG. 13;

FIG. 14(b) illustrates a diagram of another embodiment of an RB or RBpair that is communicated according to the method depicted in FIG. 13;

FIG. 15(a) illustrates a diagram of a yet another embodiment of an RB orRB pair that is communicated according to the method depicted in FIG.13;

FIG. 15(b) illustrates a diagram of a yet another embodiment of an RB orRB pair that is communicated according to the method depicted in FIG.13;

FIG. 16(a) illustrates a diagram of an embodiment of an RB or RB pairthat includes resource allocations that are selectively allocated toantenna ports that do not have overlapping DMRSs;

FIG. 16(b) illustrates a diagram of another embodiment of an RB or RBpair that includes resource allocations that are selectively allocatedto antenna ports that do not have overlapping DMRSs;

FIG. 16(c) illustrates a diagram of yet another embodiment of an RB orRB pair that includes resource allocations that are selectivelyallocated to antenna ports that do not have overlapping DMRSs;

FIG. 16(d) illustrates a diagram of yet another embodiment of an RB orRB pair that includes resource allocations that are selectivelyallocated to antenna ports that do not have overlapping DMRSs;

FIG. 17 illustrates a flowchart of another embodiment of a method fortransmitting an RB or RB-pair carrying an E-PDCCH;

FIG. 18 illustrates a flowchart of a method for receiving the RB or RBpair communicated by the method depicted in FIG. 17; and

FIG. 19 illustrates a block diagram of an embodiment of a communicationsdevice.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently described embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention. Forexample, embodiments generally are described for evolved NodeBs (eNBs)and user equipments (UEs) for LTE rel-11 and later, but embodiments maybe applied to other types of wireless communications systems such asIEEE 802.16.

An issue relates to a zero power problem that may arise when the E-PDCCHcomprises two eCCEs or two resource partitions associated with antennaports whose reference signals span the same REs (e.g., antenna port 7and 8, etc.). Some aspects of this disclosure may be discussed in thecontext of 3GPP LTE-A release-10 (and other LTE standards). However,aspects of this disclosure are not so limited, and may be applicable toother contexts as well. As an example, a zero power problem may occurwhen a DMRS (in accordance with the 3GPP LTE-A release-10 standard)intended for a PDSCH is used for E-PDCCH. DMRS with antenna ports 7, 8,9, 10, 11, 12, 13, 14 have been defined in 3GPP 36.211 release 10. Asillustrated in FIG. 6, the DMRSs for antenna ports 7 and 8 arecode-division multiplexed, and the DMRSs of antenna ports 9 and 10 arealso code-division multiplexed. Conversely, for example, the DMRSs ofantenna ports 7 and 9 are time-frequency orthogonal. The Walsh code usedfor a DMRS is <a,b,c,d>, which is modulated in the REs of DMRS asindicated in FIG. 6. DMRS of Antennna port 4 has the Walsh code<a,b,c,d>=<1,1,1,1>, DMRS of antenna port 5 has the Walsh code<a,b,c,d>=<1,−1,1,−1>.

In LTE, each eCCE or resource partition may be associated with anantenna port that corresponds to a specific set of spatial resources,for example a beamforming vector or a precoding vector in the spatialdomain. To facilitate demodulation, each eCCE or resource partition istypically accompanied by a reference signal (e.g., transmitted in thesame RB or RB-pair) that is pre-associated with the correspondingantenna port. These reference signals may be known signals (e.g., aknown Walsh sequence) that are detected by the UE for purposes ofestimating channel characteristics (e.g., fading, etc.). Because eachresource partition may be associated with a different antenna port, anRB pair carrying multiple eCCEs may typically also carry a separatereference signal for each eCCE. For instance, an RB-pair carrying aneCCE0 and an eCCE1 corresponding to antenna ports 7 and 8 (respectively)may typically carry two separate demodulation reference signals(DMRS)—one for antenna port 7 and another for antenna port 8. In oneembodiment, multiple eCCEs in an RB-pair may be allocated to multipleE-PDCCHs in order to carry multiple control messages in the RB pair. Inthe same or other embodiments, multiple eCCEs in an RB-pair may beallocated to one E-PDCCH in order to ensure better performance for thesingle E-PDCCH. However, a zero power problem occurs when an E-PDCCH isallocated multiple resource partitions whose reference signals span thesame REs. For instance, an RB (or RB-pair) carrying a DMRS for antennaport 7 and a DMRS for antenna port 8 (both of which being allocated tothe same E-PDCCH) would have a zero power problem, as the second andfourth symbols of the respective Walsh codes <1,1,1,1> and <1,−1,1,−1>would, in effect, cancel one another out (i.e., result in <2,0,2,0>).This zero power problem is undesirable in so far as it inhibits channelestimation by the UE. As such, mechanisms and/or techniques for avoidingthe aforementioned zero power problem are desired.

Some aspects of this disclosure disclose techniques for evenlypartitioning an RB (or RB-pair) into two or more control channelelements (CCEs), one or more of which may be designated as an enhancedcontrol channel element (eCCE) for carrying an E-PDCCH (or portionthereof). Specifically, a checkerboard partitioning technique is used toassign (or partition) available REs (e.g., REs not reserved foroverhead) to a first control channel element (e.g., an eCCE0) and asecond control channel element (e.g., an eCCE1). Notably, thischeckerboard partitioning technique achieves an even apportionment ofavailable REs between the eCCE0 and the eCCE1 irrespective of the amountand/or positioning of overhead in the RB (or RB-pair). Additionally,this checkerboard partitioning technique can be used for partitioning anRB (or RB-pair) amongst three or more control channel elements (e.g.,three eCCEs, four eCCEs, etc.)

Other aspects of this disclosure suggest techniques for avoiding a zeropower problem when an RB or RB-pair comprises two (or more) controlchannel elements whose corresponding respective reference signals spanthe same or common REs. In one embodiment, the zero power problem isavoided by selecting one of the reference signals for channelestimation, and then including the selected reference signal in the RB(or RB-pair), while omitting the unselected reference signal from the RB(or RB-pair). For instance, when an RB or RB-pair comprises two controlchannel elements corresponding to antenna ports 7 and 8 (respectively),the DMRS corresponding to antenna port 7 may be selected for E-PDCCHchannel estimation, and the DMRS corresponding to antenna port 8 may beomitted (i.e., not transmitted in the RB or RB-pair for the E-PDCCH).Upon reception of the E-PDCCH, the UE may be configured to use the DMRScorresponding to antenna port 7 to perform channel estimation for thetwo resource partitions of the E-PDCCH (i.e., including the portion ofthe E-PDCCH carrying to the second resource partition corresponding toantenna port 8). Alternatively, the DMRS corresponding to antenna port 8may be selected, and the DMRS corresponding to antenna port 7 may beomitted (i.e., not transmitted in the RB or RB-pair for the E-PDCCH).

In another embodiment, the zero power problem may be avoided by using anI, Q multiplexing technique to combine the respective reference signalsinto a complex reference signal, which may then be transmitted in thecommon REs. Specifically, the I, Q multiplexing technique may apply aphase shift to one of the reference signals such that the two referencesignals may be multiplexed together to form a complex reference signal.For instance, the DMRSs for antenna ports 7 and 8 may be combined bymultiplying the DMRS for antenna port 8 by a complex constant having aphase shift of π/2, and then multiplexing the phase-shifted DMRS forantenna port 8 with the DMRS for antenna port 7. As a result, the DMRSfor antenna port 7 <1, 1, 1, 1> and the modified DMRS for antenna port 8<j, −j, j, −j> combine to generate a complex DMRS <1+j, 1−j, 1+j, 1−j>,which may then be transmitted in the common REs to avoid theaforementioned zero power problem.

FIG. 1 illustrates a wireless network 100 comprising a cellular coveragearea 101 within which an eNB 110 provides wireless access to a pluralityof UEs 115, 125. The eNB 110 may provide wireless access by establishingdownlink communication links (solid arrows) and uplink communicationlinks (dashed arrows) with the UEs 115, 125. In an embodiment, thewireless network 100 may operate in accordance with an LTE communicationprotocol. In such an embodiment, the downlink communications may includea PDCCH, a PDSCH, and an E-PDCCH, while the uplink communicationschannel may include a data channel (e.g., a physical uplink sharedchannel (PUSCH). The PDSCH and PUSCH may include network resources(e.g., time-frequency resources in the form of blocks (RBs)), which maybe assigned to the UEs 115, 125 through signaling carried in the PDCCHand/or the E-PDCCH.

FIG. 2 illustrates a block of time-frequency resources 200 for carryingdownlink communications over the downlink communication link. As shown,the block of time-frequency resources 200 are segmented into a controlregion 210 and a data region 220. The control region 210 is occupied bya PDCCH 212, while the data region 220 is occupied by an E-PDCCH 222 anda PDSCH 224. The E-PDCCH 222 may be used for carrying uplink anddownlink grant information. In some embodiments, the E-PDCCH 222 mayextend into the control region 210.

As mentioned above, one challenge in implementing the E-PDCCH is toevenly partition an RB (or RB-pair) amongst multiple control channelelements. Specifically, and in accordance with aspects of thisdisclosure, even apportionment of the RB pair (or RB-pair) is achievedusing a checkerboard partitioning technique. FIG. 3 illustrates an RB300 that has been evenly partitioned using to a checkerboardpartitioning technique. As shown, the RB 300 comprises a plurality ofREs, which are classified as either overhead REs (dotted squares) oravailable RS (striped squares). The overhead REs in the RB 300 isreserved for carrying overhead information, such as reference signalsused for channel estimation. The available REs in the RB 300 carrycontrol information (e.g., grant information) of an E-PDCCH. Theavailable REs are evenly partitioned between a first control channelelement mapping to an eCCE0 index and a second control channel elementmapping to an eCCE1 index. For purposes of clarity and concision,control channel elements may be referred to as eCCEs throughout thisdisclosure. In some embodiments, the eCCE0 and eCCE1 may carry grantinformation for the same UE, while, in other embodiments, the eCCE0 andeCCE1 may carry grant information for different UEs.

Notably, the RB 300 is evenly partitioned such that equal numbers ofavailable REs are allocated to the eCCE0 and the eCCE1, resulting in acheckerboard type pattern. When there are two control channel elementseCCE0 and eCCE1, checkerboard partitioning is achieved by assigning tothe eCCE0 all available REs that occupy odd timeslots spanning oddsub-carrier frequencies, and all available REs that occupy eventimeslots spanning even sub-carrier frequencies, while assigning to theeCCE1 all remaining available REs (e.g., all available REs occupyingeven timeslots spanning odd sub-carrier frequencies and odd timeslotsspanning even sub-carrier frequencies).

Advantageously, the checkerboard partitioning technique achieves evenpartitioning irrespective of the overhead pattern/configuration. FIG. 4illustrates an RB 400 carrying resource allocations mapping to the eCCE0and the eCCE1. As shown, the RB 400 is evenly partitioned between theeCCE0 and the eCCE1, even though the RB 400 has a different overheadconfiguration than the RB 300. Hence, the checkerboard partitioningtechnique achieves even partitioning irrespective of the overheadpattern/configuration.

Additionally, the checkerboard partitioning technique is adaptable foran RB or RB-pair carrying three or more control channel elements. FIG. 5illustrates an RB 500 carrying an four control channel elements,including an eCCE0, an eCCE1, an eCCE2, and an eCCE3. As shown, theavailable REs of the RB 500 are evenly apportioned amongst the fourcontrol channel elements (eCCE0-eCCE3) using an adapted version of thecheckerboard partitioning technique. Notably the checkerboardpartitioning technique may be further adapted to evenly partition theavailable REs of an RB (or RB-pair) amongst three control channelelements, as well as amongst five or more control channel elements. Thecheckerboard partitioning technique may also be implemented to partitionan RB or RB-pair into regions for carrying distinct channels. Forinstance, an RB or RB-pair could be partitioned such that an E-DPCCH maybe multiplexed with a PDSCH.

An eCCE is associated with an antenna port (AP) so that the UE knowswhere to look for the DMRS sequence in the RB or RB-pair, and whichOrthogonal Cover Code (OCC) to use for channel estimation. Specifically,the eNB assigns APs to eCCEs based on an AP-to-eCCE mapping rule, whichis known by (or communicated to) the UE. Accordingly, the UE applies theAP-to-eCCE mapping rule to identify which AP to use when attempting todecode an E-PDCCH/eCCE based on the RE location. The AP-to-eCCE mappingrule may be communicated by higher layer signaling, or may be a prioridetermined and written in the standard specification documents.

With this AP-to-eCCE mapping rule, each eCCE is mapped to an AP (e.g.,one AP for each eCCE), and hence an RB or RB-pair carrying multipleeCCEs also carries multiple reference signals (as identified by the APsmapped to the eCCEs). Including multiple reference signals within an RBor RB-pair may be advantageous in some situations (e.g., when an E-PDCCHis transmitted using a diversity mode). However, in other situations, itmay be preferable to use a single reference signal. In such situations,a pre-defined rule may be implemented so that one AP is used formultiple eCCEs of a single E-PDCCH transmission. For instance, the UEmay use the AP associated with the eCCE with the lowest index.

Further and as mentioned above, another challenge when implementing theE-PDCCH relates to a zero power problem that occurs when an RB orRB-pair carries two reference signals that span common REs.Specifically, when an RB or RB-pair carries two or more control channelelements (e.g., each of which being associated with a different antennaport), the RB or RB-pair also carries a separate reference signal (e.g.,DMRS or otherwise) for each control channel element (e.g., so that theUE can perform channel estimation). When the RB or RB-pair carries tworeference signals that span common REs, the symbols of the respectivereference signals may cancel one another out, thereby causing a zeropower problem to occur. FIG. 6 illustrates a model RB 600 for carryingreference signal symbols for antenna ports 7, 8, 9, and 10 of the LTEfamily of communications protocols. As shown, the respective DMRSs forantenna ports 7 and 8 span the same REs, and the REs for antenna ports 9and 10 span the same REs. The Walsh Codes <a, b, c, d> for antenna ports9-10 are as follows: antenna port 7 <1, 1, 1, 1>; antenna port 8 <1, −1,1, −1>; antenna port 9 <1, 1, 1, 1>; and antenna port 10 <1, −1, 1, −1>.

Notably, the zero power problem generally arises when the two controlchannel elements associated with conflicting reference signals areintended for a single user. That is to say, the zero power problem maynot be present when the control channel elements associated withconflicting reference signals are intended for different users, becausethe conflicting reference symbols may be differentiated from one anotherin the code domain (e.g., such as by multiplying different constants).

FIGS. 7 and 8 illustrate two examples of how the zero power problemarises in conventional LTE frames. FIG. 7 illustrates an RB 700 carryingan eCCE0 and an eCCE1 corresponding to antenna ports 7 and 8(respectively). As shown, a zero power problem occurs when the DMRS forantenna port 7 (e.g., <1, 1, 1, 1>) and the DMRS for antenna port 8(e.g., <1, −1, 1, −1>) are transmitted together in the RB 700, as theREs carrying symbols b and d have zero amplitude. FIG. 8 illustrates howa similar problem occurs when an RB 800 carries an eCCE0 and an eCCE1corresponding to antenna ports 9 and 10 (respectively).

One solution to the zero power problem is to select one of the tworeference signals to use for channel estimation, and omit the unselectedreference signal from the RB or RB-pair entirely. Notably, discussionsrelating to the omission of a reference signal from an RB or RB-pair maybe in the context of a single code domain, e.g., as might be assigned toa single user, and therefore should not be interpreted as preventing theunselected reference signal from being transmitted in the RB or RB-pairin a different code domain, e.g., as might be assigned to another user.

FIG. 9 illustrates a method 900 for RB or RB-transmission, whichincludes selecting one of two overlapping reference signals for channelestimation to avoid the zero power problem that plagues the prior art.The method 900 begins at step 910, where an eNB partitions an RB orRB-pair amongst an eCCE0 and an eCCE1. The eCCE0 and the eCCE1 areassociated with separate antenna ports. Next, the method 900 proceeds tostep 920, where eNB determines that the reference signals pre-assignedto the antenna ports span common REs. For instance, it may be determinedthat the eCCE0 and the eCCE1 are associated with antenna ports 7 and 8(respectively), or, alternatively, with antenna ports 9 and 10(respectively). Next, the method 900 proceeds to step 930, where one ofthe two reference signals is selected for channel estimation. Theselected reference signal will be included in the RB or RB-pair, andwill be used to perform channel estimation for both the eCCE0 and eCCE1,while the unselected reference signal will be omitted from (i.e., nottransmitted in) the RB or RB-pair and, therefore, will not be availablefor channel estimation. The method 900 then proceeds to step 940, wherethe selected reference signal is transmitted in the RB or RB-pair.

FIG. 10 illustrates a method 1000 for receiving RB or RB-pairtransmitted by the method 900. The method 1000 begins at step 1005,where the UE receives the RB or RB-pair. Next, the method 1000 proceedsto step 1010, where the UE determines that the RB or RB-pair is carryingtwo control channel elements, namely an eCCE0 and an eCCE1. Next, themethod 1000 proceeds to step 1020, where the UE determines that theeCCE0 and eCCE1 are associated with a first reference signal and asecond reference signal (respectively). Next, the method 1000 proceedsto step 1030, where the UE determines whether the first reference signaland the second reference signal span common REs.

If the determination in step 1030 is that the respective referencesignals span the same REs, then the method 1000 proceeds to step 1040,where the UE determines which of the two reference signals was selectedfor channel estimation. In some embodiments, this determination may bemade according with a predefined rule. For instance, the pre-definedrule may state that if resource allocations corresponding to antennaports 7 and 8 are transmitted in the same RB or RB-pair, then the DMRScorresponding with antenna port 7 will be selected for channelestimation. Thereafter, the method 1000 proceeds to step 1045, where theUE performs channel estimation using the selected reference signal.Performing channel estimation may include detecting the selectedreference signal to determine channel fading and/or other channelcharacteristics of the air channel.

If the determination in step 1030 is that the respective referencesignals do not span the same REs, then the method 1000 proceeds to step1050, where the UE uses the first reference signal to perform channelestimation on the eCCE0. Thereafter, the method 1000 proceeds to step1055, where the UE uses the second reference signal to perform channelestimation on the eCCE1.

FIG. 11(a) illustrates an embodiment of an RB 1100 that is communicatedaccording to the method 900. The RB 1100 carries an eCCE0 correspondingto antenna port 7 and an eCCE1 corresponding to antenna port 8. In thisexample, the DMRS corresponding to antenna port 7 is selected forchannel estimation, and therefore is transmitted in the RB 1100. TheDMRS corresponding to antenna port 8 remains unselected, and istherefore not transmitted in the RB 1100.

FIG. 11(b) illustrates an embodiment of an RB 1150 that is communicatedaccording to the method 900. The RB 1150 carries an eCCE0 correspondingto antenna port 7 and an eCCE1 corresponding to antenna port 8. In thisexample, the DMRS corresponding to antenna port 8 is selected forchannel estimation, and therefore is transmitted in the RB 1150. TheDMRS corresponding to antenna port 7 remains unselected, and istherefore not transmitted in the RB 1150.

FIG. 12(a) illustrates an embodiment of an RB 1200 that is communicatedaccording to the method 900. The RB 1200 carries an eCCE0 correspondingto antenna port 9 and an eCCE1 corresponding to antenna port 10. In thisexample, the DMRS corresponding to antenna port 9 is selected forchannel estimation, and therefore is transmitted in the RB 1200. TheDMRS corresponding to antenna port 10 remains unselected, and istherefore not transmitted in the RB 1200.

FIG. 12(b) illustrates an embodiment of an RB 1250 that is communicatedaccording to the method 900. The RB 1250 carries an eCCE0 correspondingto antenna port 9 and an eCCE1 corresponding to antenna port 10. In thisexample, the DMRS corresponding to antenna port 10 is selected forchannel estimation, and therefore is transmitted in the RB 1250. TheDMRS corresponding to antenna port 9 remains unselected, and istherefore not transmitted in the RB 1250.

Another solution to the zero power problem is to combine the respectivereference signals (e.g., using I, Q multiplexing techniques) into acomplex reference signal. FIG. 13 illustrates a method 1300 for RB orRB-pair transmission, which includes combining overlapping referencesignals into a complex reference signal. The method 1300 begins at step1310, where an eNB partitions an RB or RB-pair into an eCCE0 and aneCCE1. The eCCE0 and eCCE1 are associated with separate antenna ports.Next, the method 1300 proceeds to step 1320, where the eNB determinesthat the pre-assigned reference signals span common REs. Thereafter, themethod 1300 proceeds to step 1330, where the first reference symbol ismultiplied by a first complex constant. Next, the method 1300 proceedsto step 1340, where the second reference symbol is multiplied by asecond complex constant having a π/2 phase difference with respect tothe first complex constant. In some embodiments, the first complexconstant may have a zero phase shift, and the second complex constantmay have a π/2 phase shift. Thereafter, the method 1300 proceeds to step1350, where the first modified reference signal and the second modifiedreference signal are multiplexed to achieve a complex reference signal.Subsequently, the method 1300 proceeds to step 1360, where the complexreference signal is transmitted in the RB or RB-pair.

FIG. 14(a) illustrates an embodiment of an RB 1400 that is communicatedaccording to the method 1300. The RB 1400 carries an eCCE0 correspondingto antenna port 7 and an eCCE1 corresponding to antenna port 8. In thisexample, the DMRS corresponding to antenna port 8 is multiplied by acomplex constant having a phase shift of π/2 such that the complexreference signal <1+j, 1−j, 1+j, 1−j> is communicated in the RB 1400.

FIG. 14(b) illustrates an embodiment of an RB 1450 that is communicatedaccording to the method 1300. The RB 1450 carries an eCCE0 correspondingto antenna port 7 and an eCCE1 corresponding to antenna port 8. In thisexample, the DMRS corresponding to antenna port 7 is multiplied by acomplex constant having a phase shift of π/2 such that the complexreference signal <1+j, −1+j, 1+j, −1+j> is communicated in the RB 1450.

FIG. 15(a) illustrates an embodiment of an RB 1500 that is communicatedaccording to the method 1300. The RB 1500 carries an eCCE0 correspondingto antenna port 9 and an eCCE1 corresponding to antenna port 10. In thisexample, the DMRS corresponding to antenna port 10 is multiplied by acomplex constant having a phase shift of π/2 such that the complexreference signal <1+j, 1−j, 1+j, 1−j> is communicated in the RB 1500.

FIG. 15(b) illustrates an embodiment of an RB 1550 that is communicatedaccording to the method 1300. The RB 1550 carries an eCCE0 correspondingto antenna port 9 and an eCCE1 corresponding to antenna port 10. In thisexample, the DMRS corresponding to antenna port 9 is multiplied by acomplex constant having a phase shift of π/2 such that the complexreference signal <1+j, −1+j, 1+j, −1+j> is communicated in the RB 1550.

Generally, two codes c*<1,1,1,1>, c*<j,−j,j,−j> can be used formultiplexing two DMRS. “c” is a complex constant. “j” is used toindicate the imaginary part of a complex number.

Another technique for avoiding the aforementioned zero power problem isto allocate, to the control channel elements, antenna ports havingnon-conflicting reference signals (i.e., reference signals whose symbolsdo not overlap in the time-frequency domain). FIG. 16(a) illustrates anembodiment of an RB 1610 that carries an eCCE0 and an eCCE1. As shown,the eCCE0 has been allocated to antenna port 7 and the eCCE1 has beenallocated to antenna port 9. Since antenna ports 7 and 9 are associatedwith non-overlapping DMRSs, there is no zero power problem in the RB1610.

FIG. 16(b) illustrates an embodiment of an RB 1620 that carries an eCCE0and an eCCE1. As shown, the eCCE0 has been allocated to antenna port 7and the eCCE1 has been allocated to antenna port 10. Since antenna ports7 and 10 are associated with non-overlapping DMRSs, there is no zeropower problem in the RB 1620.

FIG. 16(c) illustrates an embodiment of an RB 1630 that carries an eCCE0and an eCCE1. As shown, the eCCE0 has been allocated to antenna port 8and the eCCE1 has been allocated to antenna port 9. Since antenna ports8 and 9 are associated with non-overlapping DMRSs, there is no zeropower problem in the RB 1630.

FIG. 16(d) illustrates an embodiment of an RB 1640 that carries anE-PDCCH that comprises an eCCE0 and an eCCE1. As shown, the eCCE0 hasbeen allocated to antenna port 8 and the eCCE1 has been allocated toantenna port 10. Since antenna ports 8 and 10 are associated withnon-overlapping DMRSs, there is no zero power problem in the RB 1640.

Another technique for avoiding the aforementioned zero power problem isto assign a common antenna port to each control channel element in anE-PDCCH, such that a common DMRS is used to perform channel estimationfor the entire E-PDCCH. An antenna port is an index assigned to a DMRSto differentiate that DMRS from other DMRSs. The resource partition andits corresponding DMRS with the same antenna port have the same virtualantenna, and hence the same channel response after precoding.

In some embodiments, signaling may be used to inform UEs that one ormore antenna ports are associated with a resource partition (or eCCE).In the same or other embodiments, one or more antenna ports may beassociated with a resource partition (or eCCE) in a standardizedspecification (e.g., 3GPP LTE rel-11), or otherwise pre-configuredaccording to a parameter, e.g., a UE identity (C-RNTI in 3GPP) and/or asubframe number, etc. Generally, an eCCE may comprise one or moreresource partitions. As an example, in FIG. 16(a), the antenna port 7and antenna port 9 for respective CCEs may be predefined inspecification or pre-configuration according to UE identity (C-RNTI in3GPP).

In the eNodeB side, the eNodeB select the resource partitions such aseCCEs to transmit an E-PDCCH. The eNodeB may select one eCCE to transmitthe E-PDCCH, or may select multiple eCCE(2,4 eCCEs, etc) to transmit theE-PDCCH. The eNodeB transmits the E-PDCCH. In some embodiments, the UEblindly detects the control channel based on a mapping between resourcepartitions and the DMRS. In other words, the UE uses the correspondingDMRS of a resource partition (e.g., a eCCE) for channel estimation ofthe resource partition (e.g., the eCCE). Two or more resource partitionsfor control channels can be multiplexed in the same RB or RB pair.

FIG. 17 illustrates an embodiment of a method 1700 for E-PDCCHtransmission. The method 1700 begins at step 1710, where an eNBpartitions an RB (or RB-pair) into multiple eCCEs. Next, the methodproceeds to step 1720, where each eCCE in the RB (or RB-pair) isassigned an AP. The AP is an index used to differentiate different DMRSsfrom one another, and hence each eCCE is assigned an AP corresponding toa unique DMRS. The eCCE and its corresponding DMRS share a commonvirtual antenna, and hence have the same channel response afterprecoding. Next, the method 1700 proceeds to step 1730, where the eNBselects a set of eCCEs for carrying an E-PDCCH transmission. Thereafter,the method 1700 proceeds to step 1740, where the eNB determines a singleAP to use for the E-PDCCH channel estimation. Next, the method 1700proceeds to step 1750, where the eNB identifies a DMRS corresponding tothe AP. Finally, the method 1700 proceeds to step 1760, where the eNBmaps, encodes, and transmits the E-PDCCH and corresponding DMRS with theRB (or RB-pair).

FIG. 18 illustrates an embodiment of a method 1800 for E-PDCCHreception. The method 1800 begins at step 1810, where the UE determinesa set of eCCEs occupied by an E-PDCCH candidate. Next, the method 1800proceeds to step 1820, where the UE determines a set of APs associatedwith the set of eCCEs. Thereafter, the method 1800 proceeds to step1830, where the UE selects a single AP for the set based on apre-defined rule (e.g., selecting the AP associated with the eCCE havingthe lowest index). Next, the method 1800 proceeds to step 1840, wherethe UE performs channel estimation using the DMRS associated with thesingle AP. Next, the method 1800 proceeds to step 1850, where the UEattempts to decode the E-PDCCH candidate. DMRSs corresponding to eachresource partition of a control channel, for a UE may be signaled to theUE. Or a mapping relation between resource partitions and DMRSs may bedefined, for example, predefined in specification.

FIG. 19 illustrates a block diagram of an embodiment of a communicationsdevice 1900, which may be equivalent to one or more devices (e.g., UEs,eNBs, etc.) discussed above. The communications device 1900 may includea processor 1904, a memory 1906, a cellular interface 1910, and one ormore supplemental interfaces 1912-1914, which may (or may not) bearranged as shown in FIG. 19. The processor 1904 may be any componentcapable of performing computations and/or other processing relatedtasks, and the memory 1906 may be any component capable of storingprogramming and/or instructions for the processor 1904. The cellularinterface 1910 may be any component or collection of components thatallows the communications device 1900 to communicate using a cellularsignal, and may be used to receive and/or transmit information over acellular connection of a cellular network. The supplemental interfaces1912-1914 may be any component or collection of components that allowsthe communications device 1900 to communicate with other devices via awireless or wireline protocol.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method for decoding, comprising: determiningthat a first control channel element associated with a first controlchannel element index value and a second control channel elementassociated with a second control channel element index value are usedfor transmission of a single control channel in a wireless network;selecting a first reference signal sequence associated with at least oneantenna port (AP) for reception of the single control channel based onthe lowest control channel index value of the first control channelelement index value of the first control channel element and the secondcontrol channel element index value of the second control channelelement; and detecting a resource element of at least one resource block(RB) using the first reference signal sequence to decode the firstcontrol channel element and the second control channel element.
 2. Themethod of claim 1, wherein the single control channel is an enhancedPhysical Downlink Control Channel (E-PDCCH) of a long term evolution(LTE) sub-frame, and wherein the first control channel element and thesecond control channel element are enhanced control channel elements(eCCEs) of the E-PDCCH.
 3. The method of claim 2, further comprising: inresponse to the selection, detecting the resource element of the atleast one RB without using a second reference signal sequence associatedwith a second AP to decode the first control channel element and thesecond control channel element.
 4. The method of claim 3, furthercomprising: in response to a determination that the first controlchannel element and the second control channel element are used fortransmission of different control channels, detecting the resourceelement of the at least one RB using both the first reference signalsequence and the second reference signal sequence to decode the firstcontrol channel element and the second control channel element,respectively.
 5. The method of claim 2, wherein the step of detect aresource element of the at least one RB using the first reference signalsequence comprises: performing channel estimation for both the firstcontrol channel element and the second control channel element using thefirst reference signal sequence.
 6. A user equipment (UE) in a wirelessnetwork, comprising: a processor; and a memory comprising instructionsthat cause the processor to: determine that a first control channelelement associated with a control channel element index value and asecond control channel element associated with a second control channelelement index value are used for transmission of a control channelcarried in at least one resource block (RB) in a wireless network;select a first reference signal sequence associated a first antenna port(AP) for reception of the control channel based on the lowest controlchannel index value of a first control channel element index value ofthe first control channel element and a second control channel elementindex value of the second control channel element; and detect a resourceelement of the at least one RB using the first reference signal sequenceto decode the first control channel element and the second controlchannel element.
 7. The UE of claim 6, wherein the control channel is anenhanced Physical Downlink Control Channel (E-PDCCH) of a long termevolution (LTE) sub-frame, and wherein the first control channel elementand the second control channel element are enhanced control channelelements (eCCEs) of the E-PDCCH.
 8. The UE of claim 7, wherein theinstructions to detect the resource element of the at least one RBcomprises: instruction to detect the resource element of the at leastone RB without using a second reference signal sequence associated witha second AP to decode the first control channel element and the secondcontrol channel element.
 9. The UE of claim 8, wherein the programfurther includes instructions to: in response to a determination thatthe first control channel element and the second control channel elementare used for transmission of different control channels, detect theresource element of the at least one RB using both the first referencesignal sequence and the second reference signal sequence to decode thefirst control channel element and the second control channel element,respectively.
 10. The UE of claim 7, wherein the instructions to detecta resource element of the at least one RB using the first referencesignal sequence comprise: instructions to perform channel estimation forboth the first control channel element and the second control channelelement using the first reference signal sequence.